In integrated cellular and adhoc networks, low frequency bands dedicated to cellular operators and Millimetre Wave (mmW) bands are usually utilized. And, adhoc network is usually partially unlicensed or lightly licensed. The adhoc network is generally implemented in a flat structure or a hierarchical structure. In the hierarchical structure, devices in the network (such as access points and terminal devices) are divided into a plurality of clusters, each cluster including a cluster-head (CH) and one or more cluster-members that are slaves to the cluster-head.
A cluster-head may be compared to a small range base station that, in the absence of a cellular eNB, provides (a subset of and) similar functionality as an eNB. For example, a cluster-head can provide synchronization and radio resource management within its cluster and also act as a central node to create a tree topology for communication with the cluster. In addition, the cluster-head can also provide a relaying functionality towards other clusters or towards a cellular eNB.
In some of the integrated cellular and adhoc networks, multi-node connectivity is employed to reduce radio link failures and enhance robustness. More specifically, in order to enhance robustness and seamlessness of cluster operations, such as in radio resource management and data packet relaying, multiple cluster-heads can be used in a cluster of devices to serve the devices in the cluster. However, in some cases, when a cluster member connects to the cluster-heads at the same time, it neither knows which cluster-head can provide a better service, nor which protocol should be used in connecting to a cluster-head. Furthermore, since there are several cluster-heads in one cluster, when multiple cluster-heads use diverse (scheduled and contention based) protocols, such as Media Control Access (MAC) protocols, the connection of cluster members to the cluster-heads is problematic. As a result, failures often occur in radio links between the cluster members and the cluster-heads, and thus robustness of communication of the cluster is deteriorated.
This problem is particularly severe in case of high mobility of a cluster member, when the cluster member needs to reconnect to cluster-heads but maintain wireless connectivity (“make before break”) during mobility between cluster-heads that may employ either same or diverse MAC protocols. For example, when a cluster-head moves out of the coverage of a cellular base station (BS) into the coverage area of an mmW pico BS or a cluster member moves out of one coverage of one cluster-head, there may be some problems with the connection of the cluster member to the cluster-heads.